1. Field of the Invention
This invention relates to insulation displacement terminals made from a flat stamping in which electrical contact with a wire or other conductor is established by the edges of a slot into which an insulated conductor is inserted.
2. Description of the Prior Art
Insulation displacement electrical terminals have been employed successfully in a number of applications. An insulation displacement terminal, normally consists of a stamped and formed member in which a slot is defined by opposed edges. When an insulated wire is inserted into such a slot, the opposed edges penetrate the insulation to establish intimate electrical contact with the underlying core of the insulated conductor. Since the slot edges penetrate the insulation, an insulation displacement terminal can be employed without first having to strip the insulation surrounding the conductive core.
One of the more widely and sucessfully employed insulation displacement terminals employs a terminal in which a slot is stamped in a plate-like member with a conductor being inserted into the slot with the conductor axis locally perpendicular to the plane of the plate-like terminal. The stresses induced in the terminal are not only sufficient to penetrate the insulation surrounding the conductive core of the wire but the slot edges can score or scape metal on the conductor to establish a clean, intimate contact, substantially free from contaminants such as oxide located on the exterior of the wire.
Although conventional insulation displacement contacts have proved suitable for many applications, the fact that the wire is not trapped within the insulation displacement slot formed in the terminal has resulted in some concerns, since the wire is not positively held in place. A number of different techniques have been employed to provide strain relief to the wire so that it cannot move upwardly out of the wire slot. A number of insulation displacement connectors have employed separate plastic strain relief caps to trap the conductors in the slots. U.S. Pat. No. 4,159,158 discloses a connector in which a wire is received in an insulation displacement slot. The insulative connector housing includes projections which prevent upward movement of the wire once it has been inserted into the wire receiving slot. U.S. Pat. No. 4,097,106 discloses an insulation displacement connector in which a portion of the insulative housing is deformed to provide conductor strain relief.
Other insulation displacement terminals have employed upper and lower opposed slots to firmly trap the conductor in place. U.S. Pat. No. 4,324,450 shows the essential features of such a termination. U.S. Pat. No. 4,019,801 discloses a similar configuration in which the conductors are first inserted through holes in the terminal and the terminal is then deformed to force plate-like portions having wire engaging slots down over the wire. Note that in each of these configurations the wire is firmly retained by the terminal itself.
Another technique for providing strain relief to conductors received in an insulation displacement slot is to employ a separate strain relief member which is a part of the terminal itself. U.S. Pat. Nos. 4,456,317; 4,277,124; 4,113,341 and 4,421,375 disclose insulation displacement terminals in which a separate strain relief barrel is crimped around the conductor after termination in an insulation displacement slot.
U.S. Pat. No. 3,950,065 discloses another terminal in which the strain relief is an integral portion of the stamped and formed terminal. This insulation displacement terminal has integral retaining fingers extending from interconnecting straps extending between parallel plates with aligned wire receiving slots. The fingers are angled inwardly and keep a fully inserted wire securely retained within the slot.
U.S. Pat. No. 4,039,239 discloses an insulation displacement terminal in which a wire positioned within an insulation displacement slot is held in place after the clip, in which the slot is located, is inserted over a free standing pin to which the wire is to be interconnected.
Each of these insulation displacement terminals employ a configuration in which the wire is inserted into a slot in a terminal initially held in a fixed position. For example, the terminal will normally be retained within an insulative housing having one or more terminals positioned with outwardly facing wire receiving slots. Insulation displacement slots can also be employed in connectors in which the wire is first secured to the housing and the terminal subsequently inserted. For example, U.S. Pat. No. 3,979,615 discloses an insulation displacement terminal which is inserted into a cavity in an insulative body to engage a wire secured in slots on opposite sides of a cavity. The wire spans the cavity and when the slots engage the conductor, a sound termination is established. Since the wire is trapped between the insulative housing and the terminal, a configuration of this type normally does not require additional wire strain relief. Similar terminals are disclosed in U.S. Pat. Nos. 4,118,103; 4,130,331 and 4,132,460. U.S. Pat. No. 4,557,544 shows a similar terminal having a wire crimp barrel on the opposite end of the terminal and U.S. Pat. No. 3,977,754 discloses a four sided terminal having insulation displacement slots in opposite sides at one end and a poke in contact on the opposite end.
Although each of these terminals is suitable for use in certain applications, there remains a need for simple, cost effective means to provide strain relief to prevent wires from moving upward out of insulation displacement slots. Preferably this strain relief should be provided by the terminal itself since the use of the insulative housing to supply the strain relief could result in relative movement between the conductor and the terminal because of the relative movement between the housing and the terminal itself.